U.S. patent application number 17/022990 was filed with the patent office on 2021-01-07 for propeller impact detection and force reduction.
The applicant listed for this patent is Kitty Hawk Corporation. Invention is credited to Christopher Scott Saunders.
Application Number | 20210001978 17/022990 |
Document ID | / |
Family ID | |
Filed Date | 2021-01-07 |
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United States Patent
Application |
20210001978 |
Kind Code |
A1 |
Saunders; Christopher
Scott |
January 7, 2021 |
PROPELLER IMPACT DETECTION AND FORCE REDUCTION
Abstract
A commanded control signal is compared against an adaptive
control signal in order to detect a rotor strike by a rotor
included in an aircraft, wherein the adaptive control signal is
associated with controlling the rotor and the adaptive control
signal varies based at least in part on the commanded control
signal and state information associated with the rotor. In response
to detecting the rotor strike, a control signal to the rotor is
adjusted in order to reduce a striking force associated with the
rotor.
Inventors: |
Saunders; Christopher Scott;
(San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kitty Hawk Corporation |
Palo Alto |
CA |
US |
|
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Appl. No.: |
17/022990 |
Filed: |
September 16, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16673579 |
Nov 4, 2019 |
10814964 |
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17022990 |
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16249645 |
Jan 16, 2019 |
10507908 |
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16673579 |
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15877047 |
Jan 22, 2018 |
10246183 |
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16249645 |
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62595963 |
Dec 7, 2017 |
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Current U.S.
Class: |
1/1 |
International
Class: |
B64C 27/00 20060101
B64C027/00; B64C 27/08 20060101 B64C027/08; B64D 31/10 20060101
B64D031/10; B64D 45/00 20060101 B64D045/00; B64D 17/80 20060101
B64D017/80 |
Claims
1. An aircraft, comprising: a rotor; and a motor controller
including: a rotor strike detector configured to detect a rotor
strike including by comparing a commanded control signal and an
adaptive control signal, wherein the adaptive control signal is
associated with controlling the rotor and the comparison is based
at least in part on a degree of deviation of the adaptive control
signal from a reference signal; and a drive and control unit
coupled to the rotor and the motor controller, the drive and
control unit being configured to, in response to detecting the
rotor strike, adjust a control signal to the rotor to change a
rotation of the rotor and to reduce a striking force applied to an
object being struck by the rotor.
2. The aircraft recited in claim 1, wherein comparing the commanded
control signal and the adaptive control signal includes:
determining the reference signal based at least in part on the
commanded control signal; determining the degree to which the
adaptive control signal, which includes a sinusoidal signal,
deviates from the reference signal; comparing the degree against a
detection threshold; and in response to the degree exceeding the
detection threshold, declaring that the rotor strike has been
detected.
3. The aircraft recited in claim 1, wherein comparing the commanded
control signal and the adaptive control signal includes:
determining the reference signal based at least in part on the
commanded control signal, wherein the reference signal includes a
measurement threshold; determining the degree to which the adaptive
control signal, which includes a sinusoidal signal, deviates from
the reference signal; comparing the degree against a detection
threshold; and in response to the degree exceeding the detection
threshold, declaring that the rotor strike has been detected.
4. The aircraft recited in claim 1, wherein comparing the commanded
control signal and the adaptive control signal includes:
determining the reference signal based at least in part on the
commanded control signal, wherein the reference signal includes a
sinusoidal reference signal; determining the degree to which the
adaptive control signal, which includes a sinusoidal signal,
deviates from the reference signal; comparing the degree against a
detection threshold; and in response to the degree exceeding the
detection threshold, declaring that the rotor strike has been
detected.
5. The aircraft recited in claim 1, wherein adjusting the control
signal to the rotor includes: in response to detecting the rotor
strike, using an electrical connector to electrically disconnect
the adaptive control signal from a rotor input signal; and in
response to electrically disconnecting the adaptive control signal
from the rotor input signal, using a pull resistor to set the rotor
input signal to a known value associated with reducing the striking
force associated with the rotor.
6. The aircraft recited in claim 1, wherein adjusting the control
signal to the rotor includes: in response to detecting the rotor
strike, opening a power switch in a switched converter, wherein the
power switch is connected to a power supply at one end and the
adaptive control signal at the other end such that opening the
power switch electrically disconnects the adaptive control signal
from the power supply; and in response to detecting the rotor
strike, closing a ground switch in the switched converter, wherein
the ground switch is connected to ground at one end and the
adaptive control signal at the other end such that closing the
power switch electrically connects the adaptive control signal to
ground.
7. The aircraft recited in claim 1, wherein adjusting the control
signal to the rotor includes: in response to detecting the rotor
strike, opening a power switch in a switched converter, wherein the
power switch is connected to a power supply at one end and the
adaptive control signal at the other end such that opening the
power switch electrically disconnects the adaptive control signal
from the power supply; and in response to detecting the rotor
strike, opening a ground switch in the switched converter, wherein
the ground switch is connected to ground at one end and the
adaptive control signal at the other end such that opening the
power switch electrically disconnects the adaptive control signal
from ground.
8. The aircraft recited in claim 1, wherein adjusting the control
signal to the rotor includes: in response to detecting the rotor
strike, obtaining an altitude associated with an aircraft;
comparing the altitude against an altitude threshold; in response
to the altitude exceeding the altitude threshold, at least
temporarily adjusting the control signal to the rotor in order to
reduce the striking force associated with the rotor; and in
response to the altitude not exceeding the altitude threshold,
adjusting the control signal to the rotor in order to reduce the
striking force associated with the rotor, at least until one or
more of the following occurs: a reset or a part replacement.
9. The aircraft recited in claim 1, wherein adjusting the control
signal to the rotor includes: in response to detecting the rotor
strike, obtaining an altitude associated with an aircraft;
comparing the altitude against an altitude threshold; in response
to the altitude exceeding the altitude threshold, at least
temporarily adjusting the control signal to the rotor in order to
reduce the striking force associated with the rotor, wherein the
rotor is permitted to restart in response to a pilot restart
instruction without a reset prior to the pilot restart instruction
or a part replacement prior to the pilot restart instruction; and
in response to the altitude not exceeding the altitude threshold,
adjusting the control signal to the rotor in order to reduce the
striking force associated with the rotor, at least until one or
more of the following occurs: a reset or a part replacement.
10. The aircraft recited in claim 1, wherein adjusting the control
signal to the rotor includes: in response to detecting the rotor
strike, obtaining an altitude associated with the aircraft;
comparing the altitude against a higher altitude threshold and a
lower altitude threshold; in response to the altitude not exceeding
the lower altitude threshold, adjusting the control signal to the
rotor in order to reduce the striking force associated with the
rotor; and in response to the altitude exceeding the higher
altitude threshold, adjusting the control signal to the rotor in
order to reduce the striking force associated with the rotor,
wherein in response to the altitude exceeding the lower altitude
threshold and not exceeding the higher altitude threshold, the
striking force associated with the rotor is not reduced.
11. A method, comprising: detecting a rotor strike including by
comparing a commanded control signal and an adaptive control
signal, wherein the adaptive control signal is associated with
controlling the rotor and the comparison is based at least in part
on a degree of deviation of the adaptive control signal from a
reference signal; and in response to detecting the rotor strike,
adjusting a control signal to the rotor to change a rotation of the
rotor and to reduce a striking force applied to an object being
struck by the rotor.
12. The method recited in claim 11, wherein comparing the commanded
control signal and the adaptive control signal includes:
determining the reference signal based at least in part on the
commanded control signal; determining the degree to which the
adaptive control signal, which includes a sinusoidal signal,
deviates from the reference signal; comparing the degree against a
detection threshold; and in response to the degree exceeding the
detection threshold, declaring that the rotor strike has been
detected.
13. The method recited in claim 11, wherein comparing the commanded
control signal and the adaptive control signal includes:
determining the reference signal based at least in part on the
commanded control signal, wherein the reference signal includes a
measurement threshold; determining the degree to which the adaptive
control signal, which includes a sinusoidal signal, deviates from
the reference signal; comparing the degree against a detection
threshold; and in response to the degree exceeding the detection
threshold, declaring that the rotor strike has been detected.
14. The method recited in claim 11, wherein comparing the commanded
control signal and the adaptive control signal includes:
determining the reference signal based at least in part on the
commanded control signal, wherein the reference signal includes a
sinusoidal reference signal; determining the degree to which the
adaptive control signal, which includes a sinusoidal signal,
deviates from the reference signal; comparing the degree against a
detection threshold; and in response to the degree exceeding the
detection threshold, declaring that the rotor strike has been
detected.
15. The method recited in claim 11, wherein adjusting the control
signal to the rotor in order to reduce the striking force includes:
in response to detecting the rotor strike, using an electrical
connector to electrically disconnect the adaptive control signal
from a rotor input signal; and in response to electrically
disconnecting the adaptive control signal from the rotor input
signal, using a pull resistor to set the rotor input signal to a
known value associated with reducing the striking force associated
with the rotor.
16. The method recited in claim 11, wherein adjusting the control
signal to the rotor in order to reduce the striking force includes:
in response to detecting the rotor strike, opening a power switch
in a switched converter, wherein the power switch is connected to a
power supply at one end and the adaptive control signal at the
other end such that opening the power switch electrically
disconnects the adaptive control signal from the power supply; and
in response to detecting the rotor strike, closing a ground switch
in the switched converter, wherein the ground switch is connected
to ground at one end and the adaptive control signal at the other
end such that closing the power switch electrically connects the
adaptive control signal to ground.
17. The method recited in claim 11, wherein adjusting the control
signal to the rotor in order to reduce the striking force includes:
in response to detecting the rotor strike, opening a power switch
in a switched converter, wherein the power switch is connected to a
power supply at one end and the adaptive control signal at the
other end such that opening the power switch electrically
disconnects the adaptive control signal from the power supply; and
in response to detecting the rotor strike, opening a ground switch
in the switched converter, wherein the ground switch is connected
to ground at one end and the adaptive control signal at the other
end such that opening the power switch electrically disconnects the
adaptive control signal from ground.
18. The method recited in claim 11, wherein adjusting the control
signal to the rotor in order to reduce the striking force includes:
in response to detecting the rotor strike, obtaining an altitude
associated with an aircraft; comparing the altitude against an
altitude threshold; in response to the altitude exceeding the
altitude threshold, at least temporarily adjusting the control
signal to the rotor in order to reduce the striking force
associated with the rotor; and in response to the altitude not
exceeding the altitude threshold, adjusting the control signal to
the rotor in order to reduce the striking force associated with the
rotor, at least until one or more of the following occurs: a reset
or a part replacement.
19. The method recited in claim 11, wherein adjusting the control
signal to the rotor in order to reduce the striking force includes:
in response to detecting the rotor strike, obtaining an altitude
associated with an aircraft; comparing the altitude against an
altitude threshold; in response to the altitude exceeding the
altitude threshold, at least temporarily adjusting the control
signal to the rotor in order to reduce the striking force
associated with the rotor, wherein the rotor is permitted to
restart in response to a pilot restart instruction without a reset
prior to the pilot restart instruction or a part replacement prior
to the pilot restart instruction; and in response to the altitude
not exceeding the altitude threshold, adjusting the control signal
to the rotor in order to reduce the striking force associated with
the rotor, at least until one or more of the following occurs: a
reset or a part replacement.
20. A computer program product, the computer program product being
embodied in a non-transitory computer readable storage medium and
comprising computer instructions for: detecting a rotor strike
including by comparing a commanded control signal and an adaptive
control signal, wherein the adaptive control signal is associated
with controlling the rotor and the comparison is based at least in
part on a degree of deviation of the adaptive control signal from a
reference signal; and adjusting a control signal to the rotor to
change a rotation of the rotor and to reduce a striking force
applied to an object being struck by the rotor.
Description
CROSS REFERENCE TO OTHER APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/673,579 entitled PROPELLER IMPACT DETECTION
AND FORCE REDUCTION filed Nov. 4, 2019, which is a continuation of
U.S. patent application Ser. No. 16/249,645, now U.S. Pat. No.
10,507,908, entitled PROPELLER IMPACT DETECTION AND FORCE REDUCTION
filed Jan. 16, 2019, which is a continuation of U.S. patent
application Ser. No. 15/877,047, now U.S. Pat. No. 10,246,183,
entitled PROPELLER IMPACT DETECTION AND FORCE REDUCTION filed Jan.
22, 2018, which claims priority to U.S. Provisional Patent
Application No. 62/595,963, entitled PROPELLER IMPACT DETECTION AND
FORCE REDUCTION filed Dec. 7, 2017, all of which are incorporated
herein by reference for all purposes.
BACKGROUND OF THE INVENTION
[0002] New types of lightweight and ultra-lightweight aircraft are
being developed for recreational use, use by novice pilots, and/or
for use in new flying environments (e.g., they can take off and
land from a backyard). In some of these aircraft, the rotors have
no shield or blade and are therefore exposed. New techniques to
detect a rotor strike and reduce the rotor's force in response to
detection of a rotor strike would be desirable. Although strike
detection techniques may exist for other applications, it would be
desirable if techniques were lightweight, low cost, and/or better
suited to the various needs and/or design considerations of an
aircraft.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] Various embodiments of the invention are disclosed in the
following detailed description and the accompanying drawings.
[0004] FIG. 1 is a flowchart illustrating an embodiment of a
process to detect a rotor strike and perform an adjustment to
reduce a striking force in response to a detected rotor strike.
[0005] FIG. 2A is a diagram illustrating a top view of a
multicopter embodiment with unshielded rotors.
[0006] FIG. 2B is a diagram illustrating a front view of a
multicopter embodiment with unshielded rotors.
[0007] FIG. 3A is a block diagram illustrating an embodiment of
rotor strike detection system which uses three phase-shifted
sinusoidal signals as the adaptive control signal.
[0008] FIG. 3B is a graph illustrating an embodiment of an increase
in an adaptive control signal (comprising phase-shifted sinusoidal
signals) due to a commanded control signal.
[0009] FIG. 3C is a graph illustrating an embodiment of an increase
in an adaptive control signal (comprising phase-shifted sinusoidal
signals) due to a rotor strike.
[0010] FIG. 4 is a diagram illustrating an embodiment of an
adaptive measurement threshold which is based on a commanded
control signal.
[0011] FIG. 5 is a diagram illustrating an embodiment of an
adaptive sinusoidal reference signal which is based on a commanded
control signal.
[0012] FIG. 6 is a flowchart illustrating an embodiment of a
process to compare a commanded control signal against an adaptive
control signal in order to detect a rotor strike.
[0013] FIG. 7A is a diagram illustrating an embodiment of
electrical connectors and pull-down resistors which are used to
adjust a control signal to the rotor in order to reduce a striking
force.
[0014] FIG. 7B is a diagram illustrating an embodiment of built-in
switches in a switched converter which are used to adjust a control
signal to the rotor in order to reduce a striking force.
[0015] FIG. 8A is a flowchart illustrating an embodiment of a
process to adjust a control signal to the rotor in order to reduce
a striking force using a pull resistor.
[0016] FIG. 8B is a flowchart illustrating an embodiment of a
process to adjust a control signal to the rotor in order to reduce
a striking force using built-in switches in a switched
converter.
[0017] FIG. 9A is a diagram illustrating an embodiment of a single
altitude threshold which is used in responding to a detected rotor
strike.
[0018] FIG. 9B is a diagram illustrating an embodiment of two
altitude thresholds which are used in responding to a detected
rotor strike.
[0019] FIG. 10A is a flowchart illustrating an embodiment of a
process to adjust the control signal to the rotor in order to
reduce the striking force associated with the rotor using altitude
and an altitude threshold.
[0020] FIG. 10B is a flowchart illustrating an embodiment of a
process to adjust the control signal to the rotor in order to
reduce the striking force associated with the rotor using altitude
and an altitude threshold where a pilot is permitted to restart the
rotor.
[0021] FIG. 10C is a flowchart illustrating an embodiment of a
process to adjust the control signal to the rotor in order to
reduce the striking force associated with the rotor using two
altitude thresholds when there is a parachute system.
DETAILED DESCRIPTION
[0022] The invention can be implemented in numerous ways, including
as a process; an apparatus; a system; a composition of matter; a
computer program product embodied on a computer readable storage
medium; and/or a processor, such as a processor configured to
execute instructions stored on and/or provided by a memory coupled
to the processor. In this specification, these implementations, or
any other form that the invention may take, may be referred to as
techniques. In general, the order of the steps of disclosed
processes may be altered within the scope of the invention. Unless
stated otherwise, a component such as a processor or a memory
described as being configured to perform a task may be implemented
as a general component that is temporarily configured to perform
the task at a given time or a specific component that is
manufactured to perform the task. As used herein, the term
`processor` refers to one or more devices, circuits, and/or
processing cores configured to process data, such as computer
program instructions.
[0023] A detailed description of one or more embodiments of the
invention is provided below along with accompanying figures that
illustrate the principles of the invention. The invention is
described in connection with such embodiments, but the invention is
not limited to any embodiment. The scope of the invention is
limited only by the claims and the invention encompasses numerous
alternatives, modifications and equivalents. Numerous specific
details are set forth in the following description in order to
provide a thorough understanding of the invention. These details
are provided for the purpose of example and the invention may be
practiced according to the claims without some or all of these
specific details. For the purpose of clarity, technical material
that is known in the technical fields related to the invention has
not been described in detail so that the invention is not
unnecessarily obscured.
[0024] Various embodiments of a technique to detect a rotor strike
and respond accordingly are described herein. In some embodiments,
the process is performed by an aircraft, such as a multicopter. In
some embodiments, the technique includes comparing a commanded
control signal against an adaptive control signal in order to
detect a rotor strike by a rotor included in an aircraft, where the
adaptive control signal is associated with controlling the rotor
and the adaptive control signal varies based at least in part on
the commanded control signal and state information associated with
the rotor; in response to detecting the rotor strike, a control
signal to the rotor is adjusted in order to reduce a striking force
associated with the rotor.
[0025] FIG. 1 is a flowchart illustrating an embodiment of a
process to detect a rotor strike and perform an adjustment to
reduce a striking force in response to a detected rotor strike. In
some embodiments, the process is performed by an aircraft (e.g., a
multicopter) where the rotors have no shield or guard to prevent
the rotors from striking anything. In some applications, such
aircraft are not taking off and landing at airports and therefore
space around the aircraft may be less controlled compared to
airports during takeoff and landing. In one example, the aircraft
is a single-seat, recreational multicopter and the owner takes off
and lands from his/her backyard (e.g., where the multicopter may
strike a person, a pet, a tree, etc.).
[0026] At 100, a commanded control signal is compared against an
adaptive control signal in order to detect a rotor strike by a
rotor included in an aircraft, wherein the adaptive control signal
is associated with controlling the rotor and the adaptive control
signal varies based at least in part on the commanded control
signal and state information associated with the rotor. In one
example where the aircraft is a manned aircraft, the commanded
control signal is based on a pilot's instructions or commands
(e.g., which are received via one or more hand controls, such as a
joystick, a thumbwheel, etc.) and/or a flight controller (e.g., the
pilot is not touching the joystick and the flight computer performs
small adjustments to keep the multicopter hover in air in the same
position). In some embodiments, the aircraft has an automated
flight controller (e.g., in an unmanned aircraft with autonomous
flight capabilities) and the commanded control signal comes from
the automated flight controller. In some examples described below,
the commanded control signal conveys or otherwise indicates a
desired rotations per minute (RPMs) or a desired torque (e.g.,
associated with a particular rotor in the case of a
multicopter).
[0027] Generally speaking, a rotor strike is detected or declared
at step 100 when the adaptive control signal and the commanded
control signal do not indicate the same or similar thing (e.g.,
similar RPMs or similar torques). For example, suppose that the
pilot is not holding the joystick and so the flight controller only
makes small changes to the commanded control signal so that the
aircraft hovers in air at constant position. If, during this
period, a very large spike or increase (e.g., in torque) is
observed in the adaptive control signal, this would be flagged as a
rotor strike (at least in this example) because there was no
corresponding indicator in the commanded control signal that an
increase (e.g., in torque) was requested by the pilot and/or the
flight controller. Presumably, the rotor has hit something and this
resistance was observed by the control system and/or feedback loop,
causing the adaptive control signal to increase.
[0028] In contrast, if the pilot (who previously had not been
holding the joystick) grabbed the joystick in order start moving
(e.g., quickly), this increase or change would be reflected in the
adaptive control signal, and a spike or increase by the adaptive
control signal would not be flagged or otherwise identified as a
rotor strike because there would be a corresponding increase or
indication in the commanded control signal. More detailed examples
of how rotor strike detection is performed are described below.
[0029] At 102, in response to detecting the rotor strike, a control
signal to the rotor is adjusted in order to reduce a striking force
associated with the rotor. In some embodiments, the control signal
which is adjusted is the adaptive control signal. Alternatively, in
some other embodiments, the commanded control signal may be the
control signal which is adjusted at step 102.
[0030] In some embodiments, the adjustment to the control signal at
step 102 actively stops the rotation of the rotor (e.g., by
applying a braking instruction or braking force). For example, the
adjustment to the control signal may cause the control signal to
indicate that the rotor should rotate in the opposite direction
(e.g., acting like a braking force on the rotor). Alternatively,
the control signal to the rotor can be changed to a neutral value,
where the rotor is instructed to rotate in neither direction. In
that scenario, inertia will cause the rotor to continue rotating in
its current direction but the striking force will be reduced
because the control signal is no longer instructing the rotor to
continue rotating.
[0031] The following figures describe an exemplary aircraft which
may use the process of FIG. 1 to detect rotor strikes and reduce a
striking force generated by a corresponding rotor accordingly.
[0032] FIG. 2A is a diagram illustrating a top view of a
multicopter embodiment with unshielded rotors. In the example
shown, multicopter 200 is a single seat aircraft with 10 rotors
where the rotors have no guard or shield (e.g., for cost and/or
weight reasons) to prevent the rotors from coming into contact with
something, either while the multicopter is on the ground or in the
air. In multicopter 200, the rotors are mounted to the multicopter
at fixed positions or angles. To maneuver, the various rotors are
rotated independently of one another at different speeds. Although
not necessarily shown from this top view, the rotors are all
slightly angled (i.e., they do not rotate in a level horizontal
plane) to make the multicopter more maneuverable.
[0033] In this example, multicopter 200 takes off and lands
vertically. This feature eliminates the need for a runway (e.g.,
the multicopter can take off and land in a field, in a backyard,
etc.). After ascending vertically during takeoff, the aircraft can
switch to a forward flight mode of flight (e.g., once a desired
cruising altitude is reached) where the aircraft flies at a
constant or steady altitude. If desired, the multicopter can hover
at a constant or steady position midair.
[0034] For redundancy and to avoid a single point of failure (which
is desirable in aircraft design), each of the 10 rotors in this
example has its own set of hardware and/or electrical components
which monitor the corresponding rotor for a rotor strike. In this
example, each set of electronics independently performs the process
of FIG. 1 on its respective rotor. That way, even if one set of
electronics (e.g., associated with one rotor) fails, a rotor strike
can still be detected for another rotor and the striking force for
that rotor can be reduced.
[0035] FIG. 2B is a diagram illustrating a front view of a
multicopter embodiment with unshielded rotors. FIG. 2B shows the
same exemplary multicopter 200 from FIG. 2A but from a different
view. From this front view, the height of the rotors relative to
the ground is more readily apparent and in this example the rotors
are on the order of 2-4 feet off the ground. At this rotor height
(e.g., which is less than the average height of an adult), a rotor
strike is possible when the multicopter is on the ground and the
rotors are rotating. In some cases, a rotor strike occurs when the
multicopter is airborne but is relatively low to the ground. A
rotor strike can also occur at higher altitudes. For example, the
aircraft could be 20 feet off the ground or higher and one or more
of the rotors could strike a tree, a power or telephone line, a
bird, etc.
[0036] In the exemplary multicopter shown here, the adaptive
control signal (not shown) includes a plurality of phase-shifted
sinusoidal signals. The following figures describe an example of
this.
[0037] FIG. 3A is a block diagram illustrating an embodiment of
rotor strike detection system which uses three phase-shifted
sinusoidal signals as the adaptive control signal. In this example,
the adaptive control signal (e.g., used at step 100 in FIG. 1 to
detect a rotor strike) comprises three phase-shifted sinusoidal
signals (300) which are referred to in the following figures as the
A signal, the B signal, and the C signal. The signals are phase
shifted with respect to each other where the B signal has a
120.degree. phase offset from the A signal and the C signal has a
240.degree. phase offset from the A signal.
[0038] The phase-shifted sinusoidal signals (300) are generated in
this example by a motor controller (302) which includes a rotor
strike detector (308) and drive and control block (309). The motor
controller (and more specifically, the drive and control block)
inputs a commanded control signal (310), state information from
sensors (304), and a strike indication signal from rotor strike
detector 308 in order to generate the three phase-shifted
sinusoidal signals (300). For example, if a strike is signaled,
then the adaptive control signals may be set to values which will
"back off" the rotor's striking force (e.g., either by actively
"braking" the rotor, or by exerting no new or additional torque so
that the rotor eventually comes to a stop).
[0039] The phase-shifted sinusoidal signals (300) are passed to
rotor 306 and control the rotation of the rotor (306). For example,
as the magnitude and/or frequency of the phase-shifted sinusoidal
signals increases, the rotor (306) attempts to rotate faster and/or
with more torque. In some embodiments, the phase-shifted sinusoidal
signals (or, more generally, the adaptive control signal) can
indicate directionality of rotation. For example, one direction of
rotation may be associated with normal operation (e.g., where in
this direction the rotors provide the necessary lift for the
aircraft to fly) and the other direction of rotation may be used as
a brake (e.g., in the event a rotor strike is detected and the
system is trying to bring the rotor to a stop as fast as
possible).
[0040] The rotor (306) causes changes to the state of the rotor and
these changes are measured by sensors (304) which output state
information. In various embodiments, the state information from the
sensors may relate to a measured RPM of the rotor, a measured
torque of the rotor, etc. In various embodiments, the sensors may
include GPS, gyroscopes, accelerometers, etc. For simplicity, only
a single rotor is shown here but as FIG. 2A and FIG. 2B show, an
aircraft may include more than one rotor and rotor strike detector
and/or rotor force mitigation components may be duplicated for
redundancy and/or to avoid a single point of failure.
[0041] To detect a rotor strike, rotor strike detector (308) inputs
the commanded control signal (310) and the phase-shifted sinusoidal
signals (300). Rotor strike detector (308) is one example of a
block or component which performs step 100 in FIG. 1. In some
embodiments, if there is some change in the phase-shifted
sinusoidal signals (e.g., corresponding to an increase in the
amount of torque and/or reduction in rotations per minute) which is
not correspondingly reflected in the commanded control signal, then
a rotor strike is flagged or otherwise identified.
[0042] In some embodiments, rotor strike detector (308) may be
implemented as a field-programmable gate array (FPGA), which would
tend to permit more complex and/or powerful rotor strike detection
processing operations. Alternatively, the rotor strike detector may
be implemented using a microprocessor (e.g., where the
microprocessor is shared between a rotor strike detection process
and other flight-related processes where less complex and/or less
powerful rotor strike detection processing operations are
supported).
[0043] Depending upon the state information and the commanded
control signal, the motor controller (302) will adjust the
phase-shifted sinusoidal signals as or if needed. The following
figures show some examples of this.
[0044] FIG. 3B is a graph illustrating an embodiment of an increase
in an adaptive control signal (comprising phase-shifted sinusoidal
signals) due to a commanded control signal. In this example, the A
signal (322), B signal (324), and C signal (326) are examples of
adaptive control signals 300 in FIG. 3A. In this example, the
magnitudes of signals 322, 324, and 326 increase, as do the
frequencies of those signals, in response to the increase in the
level or value of the commanded control signal (320). For example,
a pilot may instruct the rotor or aircraft to go faster, and the
rotor or aircraft responds accordingly.
[0045] Before time t0, the level of the commanded control signal
(320) is at a first level (L0). In response to that signal level
(and because the system is behaving perfectly in this example), the
magnitudes of the three phase-shifted sinusoidal signals (322, 324,
and 326) are at the same magnitude (i.e., L0). (For convenience and
simplicity, all of the signals are shown at the same level, but the
phase-shifted sinusoidal signals may have different magnitudes or
signal levels compared to the commanded control signal.)
[0046] At time t0, the commanded control signal (320) increases to
a second, higher level (L1). In response to that increase, the
magnitudes and frequencies of the A signal (322), B signal (324),
and C signal (326) increase so that they match the level of the
commanded control signal (320) at L1. It is clear that in this
example, the observed change in the magnitude and frequency of the
A signal (322), B signal (324), and C signal (326) is due to the
commanded control signal and not (as an example) to counter an
external force.
[0047] Alternatively, the magnitude or level of the phase-shifted
sinusoidal signals could change because of a rotor strike. The
following figure shows an example of this.
[0048] FIG. 3C is a graph illustrating an embodiment of an increase
in an adaptive control signal (comprising phase-shifted sinusoidal
signals) due to a rotor strike. In this example, the commanded
control signal (340) remains at a same level (L0) the entire time.
For convenience, the same time reference (t0) is shown in this
figure as in the previous figure. In this example, the rotor
encounters some resistance due to a rotor strike. In response, even
though the commanded control signal (340) remains at the same
level, the magnitudes and frequencies of the A signal (342), B
signal (344), and C signal (346) increase so that the rotor will
attempt to apply more torque in order to counter the resistance and
satisfy the commanded control signal. It is noted that the response
to a rotor strike is unpredictable and implementation dependent and
this is just one example of how a rotor strike would affect an
adaptive control signal comprising phase-shifted sinusoidal
signals.
[0049] Returning to step 100 in FIG. 1, a scenario like the one
shown in FIG. 3B shows an example where a rotor strike would not be
declared (e.g., because the change in the phase-shifted sinusoidal
signals corresponds and/or is corroborated by the change in the
commanded control signal). In contrast, FIG. 3C shows an example of
something that would be flagged as a rotor strike (e.g., because
the change in the frequency and/or amplitude of the phase-shifted
sinusoidal signals is not due to or in response to some change in
the commanded control signal).
[0050] To differentiate between the two scenarios shown in FIGS. 3B
and 3C, a measurement threshold may be used to obtain some metric
or measurement which in turn is used to decide whether to declare a
rotor strike. The following figure shows an example of a
measurement threshold which is based on the commanded control
signal.
[0051] FIG. 4 is a diagram illustrating an embodiment of an
adaptive measurement threshold which is based on a commanded
control signal. In the example shown, the value of the measurement
threshold is based upon the value of the commanded control signal.
For this reason, the exemplary measurement threshold shown here is
an adaptive measurement threshold as opposed to a fixed measurement
threshold. In some embodiments, a fixed measurement threshold is
used (e.g., where the measurement threshold does not vary or change
with the commanded control signal).
[0052] In this example, to measure the degree to which a
(phase-shifted) sinusoidal signal (e.g., signal 322, 324, or 326 in
FIG. 3B or signal 342, 344, or 346 in FIG. 3C) is responding to
resistance from the rotor (e.g., due to a rotor strike) as opposed
to a change in the commanded control signal, the measurement
threshold takes into account the value of the commanded control
signal. As shown in FIGS. 3B and 3C, an increase in a
(phase-shifted) sinusoidal signal could come from either resistance
or the commanded control signal.
[0053] When the commanded control signal corresponds to a low RPM
value (or, alternatively, a low torque value), the measurement
threshold is set to first, lower value (400). When the commanded
control signal corresponds to a high RPM (or, alternatively,
torque) value, the measurement threshold is set to second, higher
value (410). Two scenarios are shown here but naturally more than
two measurement threshold levels or values may be used.
[0054] The measurement threshold is used to measure the degree or
amount that one or more (phase-shifted) sinusoidal signals (e.g.,
which make up the adaptive control signal) do not correspond to the
current commanded control signal. To preserve the readability of
the graph, only the A signal is shown here; the corresponding B
signal and C signal are not shown. Signal 402 shows an A signal
when the commanded control signal corresponds to a low RPM value.
An estimate or measurement of the area bounded by measurement
threshold 400 and A signal 402 is performed, which corresponds to
shaded region 404. This area (404) is compared against a second
threshold (referred to herein as a detection threshold, not shown)
and if the area exceeds this second/detection threshold, a rotor
strike is declared.
[0055] The same decision making and/or comparison is performed when
the commanded control signal corresponds to a high RPM value. In
this scenario, dotted region 414 is a measurement of the area
bounded by the measurement threshold (410) when the commanded
control signal corresponds to a high RPM value and the A signal
(412) when the commanded control signal corresponds to a high RPM
value. This area (414) is then compared against a detection
threshold (not shown) and if the detection threshold is exceeded, a
rotor strike is declared. To put it another way, by adapting the
measurement threshold to the commanded control signal, the strike
detection threshold takes into account instances when the commanded
control signal might be causing the adaptive control signal to
change to a higher RPM or higher torque value.
[0056] In some embodiments, the detection threshold is set to a
value which differentiates between normal and/or acceptable amounts
of resistance which are relatively small versus large amounts of
resistance which are probably indicative of a rotor strike. For
example, it would be desirable to differentiate between changes in
the adaptive control signal due to noise versus changes in the
adaptive control signal due to a rotor strike (e.g., where the
rotor at least temporarily slows down and/or is impeded).
[0057] Returning briefly to FIG. 3A, in some embodiments, rotor
strike detector 308 monitors the commanded control signal (310) in
real-time and updates an internal measurement threshold in
real-time. This measurement threshold is then used to detect a
rotor strike as described above. In some embodiments, rotor strike
detector 308 uses a lookup table to map the value of the commanded
control signal to a corresponding measurement threshold.
[0058] In this example, all of the signals are monitored, but a
rotor strike is able to be declared even if only one of the signals
has been processed and/or exhibits strike-like characteristics or
properties. For applications where a fast decision is desired, this
may be attractive. Alternatively, if accuracy is desired, more
signals which exhibit strike-like characteristics (e.g., at least
two signals have to exhibit strike-like characteristics) and/or
exhibiting these characteristics over a longer period may be
required before declaring a rotor strike. Although more accurate,
this may be slower and depending upon the application or design
constraints the appropriate technique may be used.
[0059] In some embodiments, instead of using a measurement
threshold to obtain a metric or value (e.g., which is then compared
against a detection threshold), a single threshold is used and
threshold crossing is used to declare a rotor strike. For example,
a rotor strike would be declared if signal 402 (412) crossed
threshold 400 (410). In various embodiments, threshold crossing
detecting may be used in combination with a fixed threshold or an
adaptive threshold (e.g., some A above the commanded control
signal).
[0060] This example of using a measurement threshold is merely one
example of how a rotor strike may be detected. In some embodiments,
some deviation from a (e.g., sinusoidal) reference signal (e.g.,
which varies depending upon the commanded control signal) may be
used to detect a rotor strike. The following figure shows an
example of this.
[0061] FIG. 5 is a diagram illustrating an embodiment of an
adaptive sinusoidal reference signal which is based on a commanded
control signal. In this example, the magnitude of the (sinusoidal)
reference signal is selected based on the level or value of the
commanded control signal. When the commanded control signal
corresponds to a low RPM (or, alternatively, torque) value, a
sinusoidal reference signal with a lower magnitude (500) is
selected. When the commanded control signal corresponds to a high
RPM value, a sinusoidal reference signal with higher magnitude
(510) is selected.
[0062] The A signals (502 and 512) are then compared against their
respective reference signals. Shaded area 504 shows the degree or
amount that A signal 502 (when the commanded control signal is at a
low RPM value) deviates from reference signal 500 (also when the
commanded control signal is at a low RPM value). Dotted area 514
shows the degree or amount that A signal 512 (when the commanded
control signal is at a high RPM value) deviates from reference
signal 510 (also when the commanded control signal is at a high RPM
value). As before, a measurement and/or estimate of the areas
(504/514) is compared against a detection threshold (not shown) and
a rotor strike is declared if the area exceeds the detection
threshold.
[0063] As in the previous example, the commanded control signal may
be monitored and the magnitude of the sinusoidal reference signal
may be adjusted in response to any changes in the commanded control
signal and/or a lookup table may be used to map the commanded
control signal to a magnitude to use for the reference signal. In
some embodiments, using a (e.g., sinusoidal) reference signal is
faster at detecting a rotor strike than using a measurement
threshold in combination with a detection threshold.
[0064] In some embodiments, a non-sinusoidal reference signal is
used. For example, a sawtooth reference signal may be used where
the signal is made of various lines for different segments.
[0065] The following figure describes the above examples more
generally and/or formally in a flowchart.
[0066] FIG. 6 is a flowchart illustrating an embodiment of a
process to compare a commanded control signal against an adaptive
control signal in order to detect a rotor strike. In some
embodiments, this process is used at step 100 in FIG. 1. Rotor
strike detector 308 shows one example of a component which may
perform the process of FIG. 6.
[0067] At 600, a reference signal is determined based at least in
part on the commanded control signal. For example, measurement
thresholds 400 and 410 from FIG. 4 are examples of a reference
signal where the value of the measurement threshold varies
depending upon the RPM (or, alternatively, torque) value indicated
by the commanded control signal. In FIG. 5, sinusoidal reference
signals 500 and 510 (e.g., where the magnitude of the reference
signal depends upon the RPM or torque value indicated by the
commanded control signal) show another example of a reference
signal which is determined at step 600.
[0068] At 602, a degree to which the adaptive control signal, which
includes a sinusoidal signal, deviates from the reference signal is
determined. For example, in FIG. 4, an estimate or measurement of
shaded area 404 or dotted area 414 is performed. In the example of
FIG. 5, shaded area 504 or dotted area 514 is measured or otherwise
estimated.
[0069] At 604, the degree is compared against a detection
threshold. For example, shaded area 404 or dotted area 414 in FIG.
4 is compared against some detection threshold. Or, shaded area 504
or dotted area 514 in FIG. 5 is compared against the detection
threshold.
[0070] At 606, in response to the degree exceeding the detection
threshold, it is declared that the rotor strike has been detected.
As described above, the detection threshold may be used to
differentiate between relatively low and/or typical amounts of
deviation (e.g., due to relatively low and/or acceptable amounts of
resistance, for example, due to noise or small errors) versus
relatively high and/or atypical amounts of deviation (e.g., due to
a rotor strike). Alternatively, if the detection threshold is not
exceeded, then no rotor strike is declared.
[0071] Returning briefly to step 102 in FIG. 1, in response to
detecting the rotor strike, a control signal to the rotor is
adjusted in order to reduce a striking force associated with the
rotor. The following figures show some examples of this.
[0072] FIG. 7A is a diagram illustrating an embodiment of
electrical connectors and pull-down resistors which are used to
adjust a control signal to the rotor in order to reduce a striking
force. In the example shown, motor controller 700 inputs a
commanded control signal (not shown) and outputs an adaptive
control signal in the form of three phase-shifted sinusoidal
signals (702).
[0073] The phase-shifted sinusoidal signals are passed to
electrical connectors 704. During normal operation, the electrical
connectors pass what is observed at the input (i.e., phase-shifted
sinusoidal signals 702) through to the output (i.e., rotor inputs
706). In this scenario, the rotor (708) would receive and be
controlled by the phase-shifted sinusoidal signals (702).
[0074] However, if a rotor strike is detected, the electrical
connectors will (e.g., at least electrically) disconnect the phase
shifted sinusoidal signals (702) from the rotor inputs (706) so
that those signals are no longer driven. In the absence of any
driving signal (e.g., when the electrical connectors (704) have
disconnected the phase-shifted sinusoidal signals (702) from the
rotor inputs (706)), the pull-down resistors (710) will pull the
rotor inputs (706) to ground. Pull-up resistors are similar to
pull-down resistors except they are connected to power as opposed
to ground and in some embodiments a pull-up resistor is used to
stop a rotor in a manner similar to that shown here. The value set
by the pull-down resistors at the rotor input (at least in this
example) corresponds to either a neutral value (e.g., where no
braking force is applied to the rotor) or a value which causes a
braking force to be applied to the rotor.
[0075] In some embodiments, the electrical connectors (704) are
reversible connectors so that (if desired) the phase-shifted
sinusoidal inputs (702) can again be passed through to the rotor
inputs (706). For example, a switch (which can be opened or closed)
can be reversed. Alternatively, the electrical connectors may
comprise irreversible connectors, such as a fuse which would need
to be replaced once it is blown.
[0076] The exemplary system is attractive for a number of reasons.
First, it is relatively inexpensive and lightweight, both of which
are attractive in low-cost, (ultra)lightweight aircraft
applications. It is also simple to implement. Again, for aircraft
applications, simplicity is desirable because it is less likely to
fail. Lastly, the system is relatively fast. Switching the
electrical connectors 704 is relatively fast, so the aircraft can
respond quickly once a rotor strike is detected (which is desirable
in case a rotor is striking a person).
[0077] The following figure shows another embodiment, where
existing components in the motor controller are used to reduce a
striking force when a rotor strike is detected.
[0078] FIG. 7B is a diagram illustrating an embodiment of built-in
switches in a switched converter which are used to adjust a control
signal to the rotor in order to reduce a striking force. In this
example, the motor controller (720) includes a switched converter.
A switched converter is a type of circuit which is used to convert
one voltage (e.g., 10 V) into another voltage (e.g., 5 V) using
switches. The exemplary switched controller actually has a total of
three pairs of switches (e.g., each of which generates a
corresponding phase-shifted, sinusoidal signal) but to preserve the
readability of the figure, only a single pair of switches is shown
here.
[0079] To generate a 5 V signal from a 10 V power supply (as an
example), the switches are opened and closed in a specific pattern.
First, power switch 724, which connects the output signal (i.e.,
the relevant one of the adaptive control signals) to the 10 V power
supply, is closed for some time t while ground switch 726 (which
connects the output signal to ground) is open. With the switches in
this position, the output signal is connected to the 10 V power
supply and not ground so that the output signal is at 10 V for a
duration of t.
[0080] Then, the switches are reversed for the same amount of time
t: the power switch (724) is opened so that the output is
electrically disconnected from the 10 V power supply, and the
ground switch (726) is closed so that the output signal is
electrically connected to ground. The causes the output signal to
be 0 V for a duration of t.
[0081] This process is repeated so that a square wave with a 50%
duty cycle is produced which alternates between 10 V and 0 V which
corresponds to a 5 V signals. These phase-shifted, sinusoidal
signals (722) produced are then passed to the rotor, where the
amplitude and phase control the rotor (e.g., the torque and
rotational speed, respectively).
[0082] If a strike is detected, these built-in switches can be used
to reducing the striking force of rotor 728. In some embodiments,
both the power switch (724) and ground switch (726) are opened so
that the output signal (i.e., one of the phase-shifted, sinusoidal
signals) is connected to neither power nor ground so that it is
floating). This floating value would cause the rotor to gradually
come to a stop (e.g., with inertia causing the rotor to continue
rotating, at least at first). Although the rotor is still spinning
(at least at first), the striking force is reduced and there is no
sudden generation of heat.
[0083] Alternatively, if a sudden, braking stop is desired, the
ground switch (726) can be closed and the power switch (724) can be
opened so that the output signal (i.e., one of the phase-shifted,
sinusoidal signals) is connected to ground. This would cause the
rotor to come to a sudden, braking stop. The downside is that a
large amount of heat would be generated (e.g., there may be a
burning smell).
[0084] A benefit to using built-in switches in a switched converter
is that it does not require new or additional parts since the motor
controller already includes a switched converter. In contrast, even
though the electrical connectors (704) and pull-down resistors
(710) in FIG. 7A may be relatively small, cheap, and/or
lightweight, they are still new or additional parts which were not
originally in the design.
[0085] The following figures describe these examples more generally
and/or formally in flowcharts.
[0086] FIG. 8A is a flowchart illustrating an embodiment of a
process to adjust a control signal to the rotor in order to reduce
a striking force using a pull resistor. In some embodiments, the
example process shown here is used at step 102 in FIG. 1.
[0087] At 800, in response to detecting the rotor strike, an
electrical connector is used to electrically disconnect the
adaptive control signal from a rotor input signal. See, for
example, electrical connectors 704 in FIG. 7A which use the rotor
strike detected signal as the control or select signal. In that
example, the adaptive control signal comprises three phase-shifted
sinusoidal signals but, naturally, in some other embodiments, the
adaptive control signal may comprise something else. As described
above, an electrical connector may be a switch, a fuse, etc.
[0088] At 802, in response to electrically disconnecting the
adaptive control signal from the rotor input signal, a pull
resistor is used to set the rotor input signal to a known value
associated with reducing the striking force associated with the
rotor. See, for example, pull-down resistors 710 in FIG. 7A. If the
electrical connectors (704) electrically disconnect the
phase-shifted sinusoidal signals (702) from the rotor inputs (706),
then the pull-down resistors will bring the rotor inputs (706) to a
known value, specifically zero or ground. A pull resistor (e.g.,
referred to in step 802) may in some other embodiments be a pull-up
resistor connected to power.
[0089] In an aircraft application, what constitutes an appropriate
response to a rotor strike being detected (e.g., at step 102 in
FIG. 1) may depend upon the altitude of the aircraft when a rotor
strike is detected. The following figures show an example of this,
where an aircraft's altitude is taken into consideration.
[0090] FIG. 8B is a flowchart illustrating an embodiment of
processes to adjust a control signal to the rotor in order to
reduce a striking force using built-in switches in a switched
converter. In some embodiments, one of the example processes shown
here is used at step 102 in FIG. 1.
[0091] At 810, in response to detecting the rotor strike, a power
switch in a switched converter is opened, wherein the power switch
is connected to a power supply at one end and the adaptive control
signal at the other end such that opening the power switch
electrically disconnects the adaptive control signal from the power
supply. For example, motor controller 720 in FIG. 7B includes a
switched controller with three pairs of switches (not all of which
are shown). All of the power switches (724) would be opened so that
adaptive control signals (722) are not connected to the power
supply.
[0092] For brevity, two processes are shown here, where the ground
switch (e.g., ground switch 726 in FIG. 7B) can either be open
(e.g., so that the adaptive control signal is floating) or closed
(e.g., so that the adaptive control signal is connected to ground)
as described above.
[0093] At 812, in response to detecting the rotor strike, a ground
switch in the switched converter is closed, wherein the ground
switch is connected to ground at one end and the adaptive control
signal at the other end such that closing the power switch
electrically connects the adaptive control signal to ground. For
example, in FIG. 7B, all of the ground switches (726) would be
closed. This would cause all of the adaptive control signals (722)
to be low (i.e., at the ground value, which would bring rotor 728
to a sudden and/or braking halt).
[0094] Alternatively, at 814, in response to detecting the rotor
strike, a ground switch in the switched converter is opened,
wherein the ground switch is connected to ground at one end and the
adaptive control signal at the other end such that opening the
power switch electrically disconnects the adaptive control signal
from ground. For example, in FIG. 7B, all of the ground switches
(726) would be opened. This would cause all of the adaptive control
signals (722) to be floating (e.g., which would bring rotor 728 to
a gradual stop).
[0095] In some embodiments, altitude and/or other state information
(e.g., associated with the aircraft overall, as opposed to the
state of one of the rotors) is used in deciding how to respond if a
rotor strike is detected. The following figures show some examples
of this.
[0096] FIG. 9A is a diagram illustrating an embodiment of a single
altitude threshold which is used in responding to a detected rotor
strike. In the example shown, aircraft 900 is at a relatively low
altitude (902) where a hard landing is relatively safe (e.g., for
the pilot and/or with respect to damage to the aircraft). For
example, the low altitude (902) may be on the order of 5-10 feet
off the ground. In this example, because a hard landing is
relatively safe at this altitude (902), the response to a rotor
strike detection can favor (if desired) reducing the striking force
of the rotor, even at the expensive of the aircraft's ability to
remain airborne.
[0097] In contrast, aircraft 904 is at a relatively high altitude
(906), for example, on the order of tens or hundreds of feet off
the ground. At this altitude, a hard landing is unsafe for the
pilot and the aircraft's ability to remain airborne is a more
important consideration than when the aircraft is at the low
altitude (902). At this high altitude (906), the response to a
rotor strike detection takes into account both the desire to reduce
the striking force of the rotor, as well as keeping the aircraft
airborne (e.g., at least to a degree necessary for a safe
landing).
[0098] For example, suppose a rotor strike is detected. The
aircraft's altitude at that time is obtained, for example, using
GPS or a downward-facing sensor such as radar, sonar, or lidar
(e.g., which is not dependent upon having a good line-of-sight
and/or communication channel to a GPS satellite). The obtained
altitude is compared against altitude threshold 908. If the
aircraft's altitude when the rotor strike is detected is below the
altitude threshold (908), the rotor's striking force is reduced in
a semi-permanent manner, for example, at least until the rotor
and/or some associated components or electronics are reset or
otherwise replaced. For example, if electronic connectors 704 in
FIG. 7 comprise fuses and the fuses were blown (e.g., because the
aircraft's altitude at the time of the rotor strike was below the
altitude threshold), then the aircraft would need to land and the
fuses would need to be replaced before that rotor could rotate
again. Alternatively, the aircraft could land and the rotor and/or
its associated components or electronics could be reset through
some user interface. In other words, reducing a rotor's striking
force in a semi-permanent manner will prevent the rotor from
restarting midair since it will need to land and components will
need to be replaced and/or reset for the rotor to be operational
again.
[0099] At higher altitudes, the ability to restart a rotor midair
(sometimes referred to herein as a flying restart) may be desirable
in order to keep the aircraft airborne or at least slow the descent
of the aircraft to the ground. In this example, if a rotor strike
is detected at an altitude above altitude threshold 908, the
rotor's striking force is reduced temporarily. For example,
immediately after a rotor strike is detected at such altitudes, the
rotor is slowed down or otherwise stopped (e.g., using a neutral
value or a braking force). If desired, the rotor is permitted to
gradually start up again, beginning at a relatively low RPM or
torque and then gradually increasing the RPM or torque. For
example, a step function of gradually increasing RPMs or torques
may be specified or otherwise passed to the rotor. If, at any point
during the step function, another rotor strike is detected, the
step function will stop and the rotor's striking force will again
be reduced (e.g., again temporarily). This may permit the aircraft
to reduce the striking force at least temporarily (e.g., giving the
pilot and/or the person or thing being struck time t0 separate)
while still getting at least some lift out of the affected rotor as
opposed to no lift from the rotor once a rotor strike is
detected.
[0100] In some embodiments, for safety reasons, a flying restart
(which in this example assumes that the aircraft's altitude is
above the altitude threshold) is only permitted if it is triggered
or otherwise initiated by a pilot. For example, it may be dangerous
to let some automated process initiate a flying restart (e.g., in
case the person or object being struck is still within striking
distance of one of the rotors). In contrast, a pilot could visually
inspect the area around the aircraft after a rotor strike is
detected, visually verify that the area surrounding the aircraft is
clear, and then restart the affected rotor (if desired).
[0101] In some embodiments, a user interface displays or otherwise
presents a flying restart button in response to a rotor strike
being detected in order to more quickly facilitate a flying restart
(e.g., so that the pilot does not have to navigate through a
sequence of pages or screens in order to find the correct page or
screen). In some embodiments, such a button is presented via a
touchscreen display. In some embodiments where the display is not a
touchscreen display, the display may indicate some sequence or
combination of inputs via the hand controls which would be
interpreted as an instruction to perform a flying restart.
[0102] In some embodiments, multiple altitude thresholds are used.
The following figure shows an example of this.
[0103] FIG. 9B is a diagram illustrating an embodiment of two
altitude thresholds which are used in responding to a detected
rotor strike. In this example, there are three altitude ranges or
zones. In the lowest range of altitudes (e.g., below the lower
altitude threshold (922)), a hard landing and/or crash is not
likely to be deadly or dangerous for the pilot (e.g., if one rotor
is stopped due to a strike being detected on that rotor or
otherwise goes out). Also, in this range of altitudes, the
multicopter could have hit a person. For this reason, in this
example, the striking force is reduced on a given rotor if a strike
is detected on that rotor (e.g., per the process of FIG. 1), for
example gradually or using a sudden, braking stop as desired.
[0104] In middle range of altitudes 924 (i.e., between the lower
altitude threshold (922) and higher altitude threshold (926), the
multicopter is at a height or altitude where it is unlikely to
strike a person. Also, in this range of altitudes, even if the
aircraft has a ballistic recovery system (i.e., a parachute system
which uses a rocket or other ballistic system to help the parachute
inflate), the aircraft is too low to the ground for the ballistic
recovery system to sufficiently slow down the aircraft. In other
words, a hard landing or crash in this range of altitudes could be
dangerous or deadly to the pilot, even if the aircraft is equipped
with a ballistic recovery system (or, more generally, a parachute
or recovery system, including non-ballistic ones that do not use
rockets or ballistics to inflate). For these reasons, in this
example, in this middle range of altitudes, the aircraft "powers
through" and does not reduce the striking force of a rotor, even if
a strike is detected at that rotor.
[0105] In the highest range of altitudes (928) above the higher
altitude threshold (926), the aircraft is unlikely to strike a
person and a ballistic recovery system would have enough time (if
deployed) to slow a falling aircraft down sufficiently to land
relatively safely. For these reasons, in this example, in this
highest range of altitudes, the striking force is reduced (e.g.,
per the process of FIG. 1).
[0106] In some embodiments (e.g., due to the likelihood of striking
a person in the highest range of altitudes and lowest range of
altitudes), the striking force of a rotor is reduced using a
sudden, braking stop in the lowest range of altitudes (920) if a
rotor strike is detected, whereas a gradual stop is used in the
highest range of altitudes (928). Both reduce the striking force of
the striking rotor, but rotor is brought to a stop after different
durations.
[0107] In some embodiments, the direction of movement is also used
to respond to a strike detection. For example, suppose that instead
of ascending straight up through the lowest range of altitudes, the
pilot decides to fly low to the ground or takes off in a diagonal
manner (e.g., simultaneously moving upwards and forwards). If so, a
strike is more likely to occur in the leading rotors. In some
embodiments, the response to a detected rotor strike depends upon
whether the rotor is a leading rotor (e.g., one of the front rotors
if the aircraft is flying forwards) or a non-leading rotor (e.g.,
one of the side or back rotors if the aircraft if flying forwards).
In some embodiments, a leading rotor is brought to a sudden,
braking halt if a strike is detected, whereas a non-leading rotor
is gradually brought to a stop. This may minimize heat generation
due to sudden, braking stops of a rotor.
[0108] These examples are described more formally and/or generally
in flowcharts below.
[0109] FIG. 10A is a flowchart illustrating an embodiment of a
process to adjust the control signal to the rotor in order to
reduce the striking force associated with the rotor using altitude
and an altitude threshold. In some embodiments, the process of FIG.
10A is used at step 102 in FIG. 1.
[0110] At 1000, in response to detecting the rotor strike, an
altitude associated with the aircraft is obtained. For example, as
described above, a variety of sensors including GPS, radar, sonar,
lidar, and such may be used to obtain the altitude of the
aircraft.
[0111] At 1002, the altitude is compared against an altitude
threshold. As described above, in various embodiments, the altitude
threshold may be used to differentiate between the type of object
being struck (e.g., at low altitudes there is a high(er) likelihood
of striking a person whereas at high altitudes there is a low(er)
likelihood of striking a person) or a safe versus unsafe height at
which to have a hard or crash landing. In some embodiments, two or
more altitude thresholds are used.
[0112] At 1004, in response to the altitude exceeding the altitude
threshold, the control signal to the rotor is at least temporarily
adjusted in order to reduce the striking force associated with the
rotor. For example, the affected rotor may be permitted (e.g.,
under certain conditions, after a certain amount of time, if so
instructed by a pilot, etc.) to do a flying restart (e.g., without
landing and/or without resetting or replacing something). As
described above, it may be safer to let the rotor restart at high
altitudes in order to prevent or otherwise mitigate a hard or crash
landing.
[0113] At 1006, in response to the altitude not exceeding the
altitude threshold, the control signal to the rotor is adjusted in
order to reduce the striking force associated with the rotor, at
least until one or more of the following occurs: a reset or a part
replacement. For example, the affected rotor would not be permitted
to restart until there was a reset or a part was replaced.
Presumably this happens on the ground and presumably this happens
after the person or object being struck is no longer in danger of
being struck.
[0114] FIG. 10B is a flowchart illustrating an embodiment of a
process to adjust the control signal to the rotor in order to
reduce the striking force associated with the rotor using altitude
and an altitude threshold where a pilot is permitted to restart the
rotor. In some embodiments, the process of FIG. 10B is used at step
102 in FIG. 1. FIG. 10B is similar to FIG. 10A and the same or
similar reference numbers are used to indicate the same or similar
steps.
[0115] At 1000, in response to detecting the rotor strike, an
altitude associated with the aircraft is obtained.
[0116] At 1002, the altitude is compared against an altitude
threshold.
[0117] At 1004', in response to the altitude exceeding the altitude
threshold, the control signal to the rotor is at least temporarily
adjusted in order to reduce the striking force associated with the
rotor, wherein the rotor is permitted to restart in response to a
pilot restart instruction without a reset prior to the pilot
restart instruction or a part replacement prior to the pilot
restart instruction. As described above, it may be safer to let a
pilot control any flying restart because the pilot can make a
visual inspection and confirm there is nothing which would be hit
by the affected rotor if that rotor were restarted.
[0118] At 1006, in response to the altitude not exceeding the
altitude threshold, the control signal to the rotor is adjusted in
order to reduce the striking force associated with the rotor, at
least until one or more of the following occurs: a reset or a part
replacement.
[0119] FIG. 10C is a flowchart illustrating an embodiment of a
process to adjust the control signal to the rotor in order to
reduce the striking force associated with the rotor using two
altitude thresholds when there is a parachute system. In some
embodiments, the process of FIG. 10C is used at step 102 in FIG.
1.
[0120] At 1010, in response to detecting the rotor strike, an
altitude associated with the aircraft is obtained.
[0121] At 1012, the altitude is compared against a higher altitude
threshold and a lower altitude threshold. As described above, in
some embodiments, below the lower altitude threshold, the aircraft
may be able to crash safely and includes altitudes where the
aircraft may strike people. In some embodiments, the higher
altitude threshold may be associated with a cutoff altitude above
which a (e.g., ballistic) recovery system is able to sufficiently
slow an aircraft down for a safe landing (and below which, the
recovery system would not have enough time t0 deploy and slow the
aircraft down sufficiently).
[0122] At 1014, in response to the altitude not exceeding the lower
altitude threshold, the control signal to the rotor is adjusted in
order to reduce the striking force associated with the rotor. See,
for example, the description of how the system responds in the
lowest range of altitudes (920) in FIG. 9B.
[0123] At 1016, in response to the altitude exceeding the higher
altitude threshold, the control signal to the rotor is adjusted in
order to reduce the striking force associated with the rotor,
wherein in response to the altitude exceeding the lower altitude
threshold and not exceeding the higher altitude threshold, the
striking force associated with the rotor is not reduced. See, for
example, the description for how the exemplary aircraft in FIG. 9B
responds to a rotor strike being detected in the highest range of
altitudes (928) and the middle range of altitudes (924).
[0124] In some embodiments, as described above, there is further
differentiation in the lowest altitude threshold (e.g., for leading
rotors versus non-leading rotors). In some embodiments, rotors in
the lowest altitude threshold are stopped immediately if a rotor
strike is detected, whereas rotors in the highest altitude
threshold are stopped gradually if a rotor strike is detected
(e.g., where both approaches would still reduce the striking force
of the rotor).
[0125] Although the foregoing embodiments have been described in
some detail for purposes of clarity of understanding, the invention
is not limited to the details provided. There are many alternative
ways of implementing the invention. The disclosed embodiments are
illustrative and not restrictive.
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